With increasing use of all dielectric cable in data communications and telecommunications systems, a need exists for reliable and economical methods for detecting dielectric cable, such as fiber optic cable and empty conduits, in underground systems. Underground conduits that are not occupied by electrical cables are difficult to locate on the surface prior to digging or trenching. Current methods for locating existing underground dielectric cable for repair and maintenance include exploratory drilling, known as posthole drilling, which is a slow and often costly and unreliable detection method that poses the risks of accidentally damaging or destroying buried cables.
Electrical wires can be inserted and energized with AC power to produce an electromagnetic field that is detectable on the surface. A detectable pull tape serves the dual purpose of enabling detecting and being useful for pulling in an electrical or fiber optic cable. Presently available detectable pull tapes are prone to abrasion related failures because the electrical wires are located on at least a portion of the outer surface of the pull tape. The tapes are abraded when threaded though the conduit grounding the signal at the point of abrasion resulting in the loss of signal over the remainder of the tape.
There are electric transmission cables with woven shielding comprising metallized warp and weft yarns to shield the conductive wires from external and internal interference. These cables would not be suitable for use as pull tapes as the warp and weft yarns would block the electromagnetic field produced by the conductive wires.
Thus, a detectable tape is needed that includes electrical conductivity and resistance sufficient to help provide reliable and accurate signal detection to locate underground cable over a long distance or a long span of conduit and will improve the durability of the electrical pathway in the pull tape.